I'm not sure about the percentage of mixed martial artists who are white, but whites certainly don't dominate at the top echelons. Of the 8 UFC men's champions, only 3 (Stipe Miocic, Conor McGregor, T.J. Dillashaw) are white. Daniel Cormier, Tyron Woodley, and Demetrius Johnson are black. Robert Whitaker and Max Holloway have Polynesian heritages (Maori and Samoan, respectively).

The UFC women's champions are a little harder to categorize. Cris Cyborg and Amanda Nunes are white latinos from Brazil. Nicco Montano is Native American (Navajo). Rose Namajunas is white (via parents from Lithuania).